Growth of Brahman cross heifers to 2 years of age in the dry tropics

Abstract

Growth of 1368 Brahman cross heifers from 6 year cohorts was monitored over the 2 years post-weaning in Australia’s northern forest, a low-animal-growth dry tropical environment. Heifers weighing 47–266 kg at weaning were managed in groups weighing <100 kg, 100–149 kg, 150–199 kg, and >199 kg during the post-weaning dry season. Weaner heifers were allocated to receive 300 g/day of a protein meal during the dry season or to basic nutritional management to sustain health. Heifers in three cohorts were allocated to first mating at 1 or 2 years of age, in four cohorts to vaccination against androstenedione, and in a small proportion of two cohorts to ovariectomy post-weaning. Growth was highly variable between seasons and years; average cohort liveweight by the start of 2-year-old mating was 256–319 kg. Heifer groups not receiving protein supplementation gained –16 to 21 kg (2 kg average) during 6-month dry seasons, and 49–131 kg (101 kg average) during wet seasons to reach an average of two-thirds of mature liveweight (445 kg) and 95% of mature hip height (1350 mm) by the start of mating at 2 years. Average body condition score (1–5) fluctuated by 1–2 units between seasons. Hip height gain continued, irrespective of season, commencing at ~0.60 mm/day at 6 months of age, and decelerating by ~0.00075 mm/day through to 2.5 years of age. Standard errors of predicted means across analyses were ~0.015 for average daily weight gains, 0.4 mm for average monthly height gain and 0.06 score units for average seasonal body condition score change. Post-weaning dry-season supplementation increased gains in liveweight, height and body condition score by an average of 0.1 kg/day, 0.1 mm/day and 0.5 units, respectively, during the supplementation period. Periods of poor nutrition or high nutritional demand secondary to reproduction suppressed daily gains in liveweight and hip height, at which times body condition score was also reduced. Subsequent to this, partial to full compensation occurred for all measures. Ovariectomy had negative effects on growth. Androstenedione vaccination had no effect on growth. The main conclusion is that heifer growth in Australia’s dry tropical northern forest region is highly variable between seasons and years, thus limiting significant proportions of some cohorts from reaching target weights for mating at 2 years of age, even after compensatory growth.

Growth and reproductive performance responses to post-weaning supplementation of early and normally-weaned Brahman crossbred heifers raised in tropical rangelands

“…This was observed approximately 1.5 years after the imposition of the supplement treatments and was contrary to our initial hypothesis. A similar response has been previously described by Fordyce and Chandra [ 61 ] as well as McLennan [ 62 ] when evaluating the effect of different supplementation strategies on growth paths of cattle raised in extensive grazing systems. These observations may indicate that the nutritional stress imposed at early weaning would not impair these heifers to achieve, at an older chronological age, a similar mature frame size of normally weaned cohorts.…”

Reproductive performance of northern Australian beef herds. 3. Descriptive analysis of major factors affecting reproductive performance

“…With B. indicus content increasing with a decreasing latitude, it was expected that cattle in the Southern and Northern Forests would be shortest and tallest respectively, as Brahmans are taller than Bos taurus types (Fordyce et al 2013); however, Northern Forest cows were as short as Southern Forest cows. This may be a function of stunting as skeletal growth is impeded by under-nutrition, exacerbated by the energy demands of pregnancy and lactation (Fordyce and Chandra 2019).…”

Defining the primary business measure of liveweight production for beef cows in northern Australia

“…When production is considered, usually measures of performance such as weaning rate are presented instead, for example, in an overview of the northe Australian beef industry (McLean et al 2014). Well-managed continuously mated Brahman-cross cows in the lowly productive, Northern forest region in which yearlings gain an average of 100-105 kg/year (McLennan 2014;Fordyce and Chandra 2017) produced 132-214 kg annually at 16-51 kg/ha, depending on stocking rate and year (Smith et al 2001). McGowan et al (2014) reported very large variation in annual liveweight production per cow in north Australian commercial beef herds (Fig.…”